SixSteps to Mushroom Farming

8/6/2019 SixSteps to Mushroom Farming

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Six Steps to

Mushroom Farming

College of Agricultural Sciences

Agricultural Research and Cooperative Extension

Daniel J. Royse1 and Robert B. Beelman21Professor of Plant Pathology,

2Professor of Food Science, The Pennsylvania State

University, College of Agricultural Sciences, University Park, PA 16803


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why water and supplements are added periodically, and the compost pile is aerated as itmoves through the turner.

Figure 1. Loose straw ready for incorporation into compost windrow (top left); compost

windrow (top right); aerated Phase I compost wharf under roof (note groves in concrete, bottom

left); grove showing aeration nozzle (bottom right, arrow).

The quality of raw materials used to make mushroom compost are highly variable and are

known to influence compost performance in terms of spawn run and mushroom yield.The geographical source of wheat straw, the variety (winter or spring) and the use of

nitrogen fertilizer, plant growth regulators and fungicides may affect compost

productivity. Wheat straw should be stored under cover to minimize growth of unwantedand potentially detrimental fungi and bacteria prior to its use to produce compost.

Gypsum is added to minimize the greasiness compost normally tends to have. Gypsum

increases the flocculation of certain chemicals in the compost, and they adhere to straw or

hay rather than filling the pores (holes) between the straws. A side benefit of this

phenomenon is that air can permeate the pile more readily, and air is essential to thecomposting process. The exclusion of air results in an airless (anaerobic) environment in

which deleterious chemical compounds are formed which detract from the selectivity ofmushroom compost for growing mushrooms. Gypsum is added at the outset of

composting at 40 lb per ton of dry ingredients.

Nitrogen supplements in general use today includes corn distillers grain, seed meals of

soybeans, peanuts, or cotton, and chicken manure, among others. The purpose of these


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supplements is to increase the nitrogen content to 1.5 percent for horse manure or 1.7percent for synthetic, both computed on a dry weight basis. Synthetic compost requires

the addition of ammonium nitrate or urea at the outset of composting to provide the

compost microflora with a readily available form of nitrogen for their growth andreproduction.

The initial compost pile should be 5 to 6 feet wide, 5 to 6 feet high, and as long as

necessary. A two-sided box can be used to form the pile (rick), although some turners areequipped with a "ricker" so a box isnt needed. The sides of the pile should be firm and

dense, yet the center must remain loose throughout Phase I composting. As the straw orhay softens during composting, the materials become less rigid and compactions can

easily occur. If the materials become too compact in the traditional Phase I process, air

cannot move through the pile and an anaerobic environment will develop. The problem ofan anaerobic center core in the compost has largely been overcome by using forced

aeration.

Turning and watering are done at approximately 2-3 day intervals, but not unless the pileis hot (145 to 170F). Turning provides the opportunity to water, aerate, and mix the

ingredients, as well as to relocate the straw or hay from a cooler to a warmer area in the

pile, outside versus inside. Supplements are also added when the compost is turned, but

they should be added early in the composting process. The number of turnings and thetime between turnings depends on the condition of the starting material and the time

necessary for the compost to heat to temperatures above 145F.

Water addition is critical since too much will exclude oxygen by occupying the porespace, and too little can limit the growth of bacteria and fungi. As a general rule, water is

added up to the point of leaching when the pile is formed and at the time of first turning,

and thereafter either none or only a little is added for the duration of composting. On thelast turning before Phase II composting, water can be applied generously so that when the

compost is tightly squeezed, water drips from it. There is a link between water, nutritivevalue, microbial activity, and temperature, and because it is a chain, when one condition

is limiting for one factor, the whole chain will cease to function.

Phase I composting lasts from 6 to 14 days, depending on the nature of the material at thestart and its characteristics at each turn. There is a strong ammonia odor associated with

composting, which is usually complemented by a sweet, moldy smell. When compost

temperatures are 155F and higher, and ammonia is present, chemical changes occurwhich result in a food rather exclusively used by the mushrooms. As a by-product of the

chemical changes, heat is released and the compost temperatures increase. Temperatures

in the compost can reach 170 to 180F during the second and third turnings when adesirable level of biological and chemical activity is occurring. At the end of Phase I thecompost should: a) have a chocolate brown color; b) have soft, pliable straws, c) have a

moisture content of from 68 to 74 percent; and d) have a strong smell of ammonia. When

the moisture, temperature, color, and odor described have been reached, Phase Icomposting is completed.


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2. Phase II: Finishing the Compost

There are two major purposes to Phase II composting. Pasteurization is necessary to kill

any insects, nematodes, pest fungi, or other pests that may be present in the compost. And

second, it is necessary to condition the compost and remove the ammonia that formed

during Phase I composting. Ammonia at the end of Phase II in a concentration higherthan 0.07 percent is often inhibitory to mushroom spawn growth, thus it must be

removed; generally, a person can smell ammonia when the concentration is above 0.10percent.

Phase II takes place in one of three places, depending on the type of production systemused. For the zoned system of growing, compost is packed into wooden trays, the trays

are stacked six to eight high, and are moved into an environmentally controlled Phase II

room. Thereafter, the trays are moved to special rooms, each designed to provide theoptimum environment for each step of the mushroom growing process. With a bed or

shelf system, the compost is placed directly in the beds, which are in the room used for

all steps of the crop culture. The most recently introduced system, the bulk system, is onein which the compost is placed in an insulated tunnel with a perforated floor and

computer-controlled aeration; this is a room specifically designed for Phase II

composting (Fig. 2).

The compost, whether placed in beds, trays, or bulk, should be filled uniformly in depthand density or compression. Compost density should allow for gas exchange, since

ammonia and carbon dioxide will be replaced by outside air.

Figure 2. Phase II tunnels used to pasteurize and condition compost for mushroom production.Left: filling machine in front of closed tunnel, Right: open tunnel ready for filling.

Phase II composting can be viewed as a controlled, temperature-dependent, ecological

process using air to maintain the compost in a temperature range best suited formicroorganisms to grow and reproduce. The growth of these thermophilic (heat-loving)

organisms depends on the availability of usable carbohydrates and nitrogen, some of the

nitrogen in the form of ammonia. These microorganisms produce nutrients or serve as


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nutrients in the compost on which the mushroom mycelium thrives and other organismsdo not.

Completing Phase II in tunnels has become more popular in recent years. Tunnel

composting has the advantage of treating more compost per ft2

compared to more

expensive production rooms. When coupled with bulk spawn run, tunnel compostingoffers the advantage of more uniformity and greater use of mechanization. However,

transfer of the finished compost from the pasteurization tunnel to the bulk spawn runtunnel may increase the risk of infestation of unwanted pathogens and pests compared to

compost that remains in the same room. Thus, higher levels of sanitation may berequired with tunnel composting compared to in-room composting.

It is important to remember the purposes of Phase II when trying to determine the proper

procedure and sequence to follow. One purpose is to remove unwanted ammonia. To thisend the temperature range from 125 to 130F is most efficient since de-ammonifying

organisms grow well in this temperature range. A second purpose of Phase II is to

remove any pests present in the compost by use of a pasteurization sequence.

At the end of Phase II the compost temperature must be lowered to approximately 75 to

80F before spawning (planting) can begin. The nitrogen content of the compost should

be 2.0 to 2.4 percent, and the moisture content between 68 and 72 percent. Also, at the

end of Phase II it is desirable to have 6 to 8 lb of dry compost per square foot of bed ortray surface to obtain profitable mushroom yields. It is important to have both the

compost and the compost temperatures uniform during the Phase II process since it is

desirable to have as homogenous a material as possible.

3. Spawning

As a mushroom matures, it produces millions of microscopic spores on mushroom gillslining the underside of a mushroom cap. These spores function roughly similar to the

seeds of a higher plant. However, growers do not use mushroom spores to seed

mushroom compost because they germinate unpredictably and therefore, are not reliable.Fortunately, mycelium (thin, thread-like cells) can be propagated vegetatively from

germinated spores, allowing spawn makers to multiply the culture for spawn production.

Specialized facilities are required to propagate mycelium, so the mushroom myceliumremains pure. Mycelium propagated vegetatively on various grains or agars is known as

spawn, and commercial mushroom farmers purchase spawn from companies specializing

in its manufacture.

Spawn makers start the spawn-making process by sterilizing a mixture of millet grainplus water and chalk; rye, wheat, and other small grain may be substituted for millet.Sterilized horse manure formed into blocks was used as the growth medium for spawn up

to about 1940, and this was called block or brick spawn, or manure spawn; such spawn is

not used today. Once sterilized grain has a bit of mycelium added to it, the grain andmycelium is shaken 3 times at 4-day intervals over a 14-day period of active mycelial

growth. Once the grain is colonized by the mycelium, the product is called spawn (Fig.

3). Spawn can be refrigerated for a few months, so spawn is made in advance of a


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farmers order for spawn.

Figure 3. Mushroom spawn from open bag (left); close up of millet spawn (right).

Spawn is distributed on the compost and then thoroughly mixed into the compost. Foryears this was done by hand, broadcasting the spawn over the surface of the compost andruffling it in with a small rake-like tool. In recent years, however, for the bed system,

spawn is mixed into the compost by a special spawning machine that mixes the compost

and spawn with tines or small finger-like devices. In a tray or batch system, spawn ismixed into the compost as it moves along a conveyer belt or while falling from a

conveyor into a tray. The spawning rate is expressed as a unit or quart per so many square

feet of bed surface; 1 unit per 5 ft2 is desirable. The rate is sometimes expressed on the

basis of spawn weight versus dry compost weight; a 2 percent spawning rate is desirable.

3.1 Supplementation at spawning

In the early 1960s, yield increases were observed when compost was supplemented with

protein and/or lipid rich materials at spawning, casing and later. Up to a 10% increase in

yield was obtained when small amounts of protein supplements were added to thecompost at spawning. Excessive heating and stimulation of competitor molds in the

compost substantially limited the amount of supplement and corresponding benefit that

could be achieved. It was these limitations that were overcome by the invention of

delayed release supplements for mushroom culture (Carroll and Schisler 1976). Thedisadvantages associated with the supplementation of non-composted nutrients to

mushroom compost at spawning were largely overcome by encapsulating micro-droplets

of vegetable oil within a protein coat that was denatured with formaldehyde. Increases ofas much as 60% were obtained. Today, several commercial supplements are available

that can be used at spawning or at casing to stimulate mushroom yield.

Amendment of mushroom substrate with Micromax is another potential opportunity forgrowers to improve the yield capacity of their Phase II compost. Micromax contains a

mixture of nine micronutrients including (percentage dry wt basis): Ca (12%), Mg (3%),

S (12%), B (0.1%), Cu (1%), Fe (17%), Mn (2.5%), Mo (0.05%), Zn (1%), and inertingredients (57.35%). Research has shown that approximately 70% of the yield increase

observed is due to Mn. Commercial supplement makers have begun to add Mn to their


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delayed release nutrients for mushroom culture.

Once the spawn and supplement have been mixed throughout the compost and the

compost worked so the surface is level, the compost temperature is maintained at 75-

80F and the relative humidity is kept high to minimize drying of the compost surface or

the spawn. Under these conditions the spawn will grow - producing a thread-like networkof mycelium throughout the compost. The mycelium grows in all directions from a spawn

grain, and eventually the mycelium from the different spawn grains fuses together,making a spawned bed of compost one biological entity. The spawn appears as a white to

blue-white mass throughout the compost after fusion has occurred. As the spawn grows itgenerates heat, and if the compost temperature increases to above 80 to 85F, depending

on the cultivar, the heat may kill or damage the mycelium and eliminate the possibility of

maximum crop productivity and/or mushroom quality. At temperatures below 74F,spawn growth is slowed and the time interval between spawning and harvesting is

extended.

3.2 Phase III and Phase IV compost

Phase III compost is Phase II compost spawn run in bulk in a tunnel, and ready for casing

when removed from the tunnel and delivered to the grower. If the Phase III compost then

is cased and the spawn allowed to colonize the casing layer before sending to the growing

unit or delivering to growers, it is called Phase IV compost. The successes of both PhaseIII and Phase IV compost depend, to a large extent, on the quality of Phase I and Phase II

composts. Use of Phase III compost may also improve mushroom quality, as

fragmentation of the colonized compost tends to improve initial color and mushroomshelf life. In recent years, the use of bulk Phase III compost has increased in popularity

because it allows an increase in the number of crops a grower can expect from his

production rooms. Phase II production on shelves allows an average of about 4.1 cropsper year whereas growers using Phase III bulk spawn run compost averages about 7.1

crops per year. An additional gain can be made in the number of crops (10-12 crops peryear) when Phase IV is used (Dewhurst 2002; Lemmers 2003; Chang 2006).

3.3 Mushroom varieties

In the United States, mushroom growers use three major mushroom cultivars: a) Smoothwhite hybrid cap smooth, cap and stalk white; b) Off-white hybrid cap scaly with

stalk and cap white; and c) Brown cap smooth, cap chocolate brown with a white stalk.

Within each of the three major groups, there are various isolates, so a grower may have achoice of up to eight strains within each variety. Generally, white and off-white hybrid

cultivars are used for processed foods like soups and sauces, but all isolates are goodeating as fresh mushrooms. In recent years, the brown varieties have gained market share

among consumers. The Crimini variety is similar in appearance to the white mushroomexcept it is brown and has a richer and earthier flavor. The Portobello variety is a large,

open, brown-colored mushroom that can have caps up to 6 inches in diameter. The

Portobello offers a rich flavor and meaty texture.

The time needed for spawn to colonize the compost depends on the spawning rate and its


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distribution, the compost moisture and temperature, compost supplementation, and thenature or quality of the compost. Complete spawn run usually requires 13 to 20 days.

Once the compost is fully-grown with spawn, the next step in production is at hand.

4. Casing

Casing is a top-dressing applied to the spawn-run compost on which the mushrooms

eventually form. A mixture of peat moss with ground limestone can be used as casing.Casing does not need nutrients since casing acts as a water reservoir and a place where

rhizomorphs form. Rhizomorphs look like thick strings and form when the very fine

mycelium fuses together. Mushroom initials, primordia, or pins form on the rhizomorphs,so without rhizomorphs there will be no mushrooms. Casing should be able to hold

moisture since moisture is essential for the development of a firm mushroom. The most

important functions of the casing layer are supplying water to the mycelium for growthand development, protecting the compost from drying, providing support for the

developing mushrooms and resisting structural breakdown following repeated watering.

Supplying as much water as possible to the casing as early as possible without leachinginto the underlying compost provides the greatest yield potential.

Sphagnum peat moss is the most commonly used material for casing. Sphagnum can

range from brown (young, less decomposed, loose textured, surface peat) to black

(compact, more decomposed, deep dug) and may be processed differently at the harvestsite. Milled peat is partially dried before packaging and transport while wet-dug peat is

transported in a saturated form. Some growers prefer wet-dug peat because of the higher

water holding capacity compared to milled peat.

Peat moss-based casing does not require pasteurization because the material is free from

pathogens, weed molds and nematodes that may reduce mushroom yield. One 6-ft3

compressed bale when mixed with water and 40 lb of limestone will cover about 125 ft2of compost surface at about 2 inches depth.

4.1 Casing inoculum (CI)

Casing inoculum is a sterilized mixture of peat, vermiculite and wheat bran that has beencolonized by mushroom mycelium. It is mixed with casing to decrease cropping cycle

time, improve uniformity of mushroom distribution over the bed and improve mushroom

cleanliness. Mycelium from the CI colonizes the casing layer while it fuses with the

underlying mycelium of the compost. This allows more breaks per crop or more cropsper year.


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Figure 4. Casing inoculum used to inoculate casing for more rapid mycelial colonization.

4.2 Supplementation at casing

The addition of nutrients at casing was first tried in the early 1960s. Results showed that

much greater amounts of nutrients could be added at casing than at spawning and thatyield increases were almost proportional to the amount added. Although yield increases

as high as 100% may be realized, certain potential problems and limitations exist for

supplementation at casing. Weed molds, nematodes and pathogens must not be present

in the compost when supplementing at casing. These organisms will be dispersedthroughout the compost when it is fragmented prior to supplementation and can multiply

very rapidly before the mushroom mycelium recovers its growth.

Managing the crop after casing requires that the compost temperature be kept at around75F for up to 5 days after casing, and the relative humidity should be high. Thereafter,

the compost temperature should be lowered about 2F each day until small mushroominitials (pins) have formed. Throughout the period following casing, water must be

applied intermittently to raise the moisture level to field capacity before the mushroom

pins form. Knowing when, how, and how much water to apply to casing is an "art form"which readily separates experienced growers from beginners.

5. Pinning

Mushroom initials develop after rhizomorphs have formed in the casing. The initials areextremely small but can be seen as outgrowths on a rhizomorph. Once an initial

quadruples in size, the structure is a pin. Pins continue to expand and grow larger through

the button stage, and ultimately a button enlarges to a mushroom (Fig. 5). Harvestablemushrooms appear 18 to 21 days after casing. Pins develop when the carbon dioxide

content of room air is lowered to 0.08 percent or lower, depending on the cultivar, by

introducing fresh air into the growing room. Outside air has a carbon dioxide content of

about 0.04 percent.


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Figure 5. Mushrooms forming and maturing on the casing a 2-inch layer of neutralized peat.

Both pins and young mushrooms are visible.

The timing of fresh air introduction is very important and is something learned only

through experience. Generally, it is best to ventilate as little as possible until the

mycelium has begun to show at the surface of the casing, and to stop watering at the timewhen pin initials are forming. If the carbon dioxide is lowered too early by airing too

soon, the mycelium will stop growing through the casing and mushroom initials formbelow the surface of the casing. As such mushrooms continue to grow, they push through

the casing and are dirty at harvest time. Too little moisture can also result in mushrooms

forming below the surface of the casing. Pinning affects both the potential yield andquality of a crop and is a significant step in the production cycle.

6. Cropping

The terms flush, break, or bloom are names given to the repeating 3- to 5-day harvestperiods during the cropping cycle; these are followed by a few days when no mushrooms

are available to harvest. This cycle repeats itself in a rhythmic fashion, and harvesting can

go on as long as mushrooms continue to mature. Most mushroom farmers harvest for 35to 42 days, although some harvest a crop for 60 days, and harvest can go on for as long as

150 days.

Air temperature during cropping should be held between 57 to 62F for good results.

This temperature range not only favors mushroom growth, but cooler temperatures can

lengthen the life cycles of both disease pathogens and insects pests. It may seem odd thatthere are pests that can damage mushrooms, but no crop is grown that does not have to

compete with other organisms. Mushroom pests can cause total crop failures, and often

the deciding factor on how long to harvest a crop is based on the level of pest infestation.

These pathogens and insects can be controlled by cultural practices coupled with the useof pesticides, but it is most desirable to exclude these organisms from the growing rooms.

The relative humidity in the growing rooms should be high enough to minimize the


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drying of casing but not so high as to cause the cap surfaces of developing mushrooms tobe clammy or sticky. Water is applied to the casing so water stress does not hinder the

developing mushrooms; in commercial practice this means watering 2 to 3 times each

week. Each watering may consist of more or fewer gallons, depending on the dryness ofthe casing, the cultivar being grown, and the stage of development of the pins, buttons, or

mushrooms. Most first-time growers apply too much water and the surface of the casingseals; this is seen as a loss of texture at the surface of the casing. Sealed casing preventsthe exchange of gases essential for mushroom pin formation. One can estimate how much

water to add after first break has been harvested by realizing that 90 percent of the

mushroom is water and a gallon of water weighs 8.3 lb. If 100 lb of mushrooms were

harvested, 90 lb of water (11 gal.) were removed from the casing; and this is what mustbe replaced before second break mushrooms develop.

Outside air is used to control both the air and compost temperatures during the harvest

period. Outside air also displaces the carbon dioxide given off by the growing mycelium.

The more mycelial growth, the more carbon dioxide produced, and since more growth

occurs early in the crop, more fresh air is needed during the first two breaks. The amountof fresh air also depends on the growing mushrooms, the area of the producing surface,

the amount of compost in the growing room, and the condition or composition of the

fresh air being introduced. Experience seems to be the best guide regarding the volume ofair required, but there is a rule of thumb: 0.3ft/ft2/hr when the compost is 8 inches deep,

and of this volume 50 to 100 percent must be outside air.

Ventilation is essential for mushroom growing, and it is also necessary to controlhumidity and temperature. Moisture can be added to the air by a cold mist or by live

steam, or simply by wetting the walls and floors. Moisture can be removed from the

growing room by: 1) admitting a greater volume of outside air; 2) introducing drier air; 3)moving the same amount of outside air and heating it to a higher temperature since

warmer air holds more moisture and thus lowers the relative humidity. Temperature

control in a mushroom growing room is no different from temperature control in your

home. Heat can originate from hot water circulated through pipes mounted on the walls.Hot, forced air can be blown through a ventilation duct, which is rather common at more

recently built mushroom farms. There are a few mushroom farms located in limestone

caves where the rock acts as both a heating and cooling surface depending on the time ofyear. Caves of any sort are not necessarily suited for mushroom growing, and abandoned

coalmines have too many intrinsic problems to be considered as viable sites for a

mushroom farm. Even limestone caves require extensive renovation and improvementbefore they are suitable for mushroom growing, and only the growing occurs in the cave

with composting taking place above ground on a wharf.

Mushrooms are harvested in a 7- to 10-day cycle, but this may be longer or shorter

depending on the temperature, humidity, cultivar, and the stage when they are picked

(Fig. 6). When mature mushrooms are picked, an inhibitor to mushroom development isremoved and the next flush moves toward maturity. Mushrooms are normally picked at a

time when the veil is not too far extended. Consumers in North America want closed,

tight, and white or brown (Crimini) mushrooms while open browns (Portobello) arepreferred by some consumers. The maturity of a mushroom is assessed by how far the


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veil is stretched, and not by how large the mushroom is. Consequently, maturemushrooms are both large and small, although farmers and consumers alike prefer

medium- to large-size mushrooms.

Figure 6. Harvesting of mushrooms. Each mushroom is hand harvested, the base of the

mushroom is trimmed, and the clean, mature mushroom placed in a basket.

Picking and packaging methods often vary from farm to farm. Freshly harvested

mushrooms must be kept refrigerated at 35 to 45F. To prolong the shelf life of

mushrooms, it is important that mushrooms "breathe" after harvest, so storage in a non-

waxed paper bag is preferred to a plastic bag.

A question frequently arises concerning the need for illumination while the mushrooms

grow. Mushrooms do not require light to grow; only green plants require light for

photosynthesis. However, growing rooms can be illuminated to facilitate harvesting orcropping practices.

Nutrients. Mushrooms are a good source of numerous nutrients. Data presented in Figure7 demonstrate this with Crimini mushrooms. They are an excellent source (contain over

20% of the RDA in a serving) of selenium, riboflavin (vitamin B2) and copper and are a

good source (contain over 10% of RDA) for niacin (vitamin B3), pantothenic acid(vitamin B5) and potassium. Criminis also contain rich amounts of thiamin (Vitamin

B1), zinc, vitamin B6, protein, folic acid, fiber, manganese and magnesium. On the other

hand, mushrooms are low in fat, sodium and calories.


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Nutrients in Crimini Mushrooms, Raw

0.1

2

2

2

3

4

5

6

7

11

13

16

20

24

31

0 10 20 30 40

sodium

manganese

magnesium

dietary fiber

folate

protein

vitamin B6

zinc

vitamin B1

potassium

vitamin B5

vitamin B3

copper

vitamin B2

selenium

3

oz-w

t(84

g)

% Daily Value

Excellent source

(>20% RDA)

Good source

(>10% RDA)

Rich in

Very low amount

Figure 7. Nutrients in crimini mushrooms based on FDA reference serving size of 84 g for raw

mushrooms. Mushrooms are not a significant source of saturated fat, trans fat, cholesterol,

sugars, vitamin A and calcium. Source: Mushroom Council.

Vitamin D. Recent research has shown that when UV light is shined on mushrooms,there is a major boost in the vitamin D2 content of the mushrooms. A single serving ofmushrooms will contain over 800% of the recommended daily allowance (RDA) of

vitamin D2 once exposed to just five minutes of UV light after being harvested. This may

be a convenient way for people who do not eat fish or drink milk to obtain their dailyrequirement of vitamin D.

Dietary fiber (DF). Mushrooms contain numerous complex carbohydrates includingpolysaccharides such as glucans and glycogen, monosaccharides, disaccharides, sugar

alcohols and chitin. Most polysaccharides are structural components of the cell walls

(chitin and glucans) and are indigestible by humans; thus they may be considered as

dietary fiber. Dietary fiber may help to prevent many diseases prevalent in affluentsocieties. Portobello mushrooms contain a higher level of DF than the white variety of

mushrooms.

Selenium. A serving (3 ounces) of Crimini mushrooms provides almost one-third of the

RDA for selenium, according to the USDA National Nutrient Database. Selenium hasbeen shown to decrease prostate cancer by more than 60% according to findings from the

Baltimore Longitudinal Study on Aging. Men with the lowest blood selenium levels


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were 4-5 times more likely to have prostate cancer than those with the highest seleniumlevels and that selenium levels tend to decrease with age.

Selenium levels can be reliably increased in mushrooms by adding sodium selenite to

mushroom compost. Some commercial supplement makers are now adding this

compound to their delayed release nutrients for mushroom culture.

Potassium. Crimini mushrooms are a good source of potassium, an element that isimportant in the regulation of blood pressure, maintenance of water in fat and muscle,

and to ensure the proper functioning of cells. A 3-ounce Portobello contains more

potassium than a banana or an orange. To date, attempts to enhance the potassiumcontent of mushrooms have met with only limited success.

Antioxidants. Portobello and Crimini mushrooms are good sources of antioxidants and

rank with carrots, green beans, red peppers and broccoli as good sources of dietaryantioxidants. They are rich sources of polyphenols that are the primary antioxidants in

vegetables and are the best source of L-ergothioneine (ERGO) a potent antioxidant only

produced in nature by fungi. Crimini mushrooms contain over 15 times more ERGOthan the previously best-known dietary sources of ERGO.

Environmental Concerns

Odors. Nuisance complaints, a result of mushroom compost preparation in close

proximity to residential areas, are a problem for some mushroom farms. Offensive odors

associated with the preparation of mushroom compost are the primary reasons for thesecomplaints. A combination of suburbanization and the heightened sensitivity of the

general population to environmental issues have focused public attention on this issue.

Growers have adopted several measures to reduce the environmental impact of

mushroom farming, including the practice of forced aeration of Phase I compostcontained in bunkers or tunnels. However, the issue of offensive odor generation

continues to place pressure on mushroom growers.

Disposal of post-crop mushroom compost. After the last flush of mushrooms has been

picked, the growing room should be closed off and the room pasteurized with steam. This

final pasteurization is designed to destroy any pests that may be present in the crop or thewoodwork in the growing room, thus minimizing the likelihood of infesting the next

crop.

Post-crop mushroom compost (MC) is the material left over after the crop has been

terminated (Fig. 8). It has many uses and is a valued product in the horticultural industry.One of the major uses of MC is for suppression of artillery fungi in landscape mulch. Theartillery fungi grow rapidly throughout moist landscape mulch, and produce sticky spore

masses about the size of a pinhead. These spores are forcibly discharged toward light

colored surfaces such as house siding and cars. Once the spores dry they are nearlyimpossible to remove without leaving an unsightly brown stain on the surface. The

incorporation of 20-40% MC into mulch effectively suppress the artillery fungi.


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Figure 8. Post-crop mushroom compost (MC) being loaded onto a truck as it is removed from a

mushroom house.

Conclusion

It takes approximately 14 weeks to complete an entire production cycle, from the start of

composting to the final steaming off after harvesting has ended. For this work a

mushroom grower can expect anywhere from 0 to 8 lb per ft2; the national average for

2006 was 5.92 lb per square foot. Final yield depends on how well a grower has

monitored and controlled the temperature, humidity, pests, and so on. All things

considered, the most important factors for good production appear to be experience plusan intuitive feel for the biological rhythms of the commercial mushroom. The production

system used to grow a crop can be chosen after the basics of mushroom growing are

understood.

Related Readings

Beelman, R.B., D.J. Royse, and N. Chikthimmah. 2004. Bioactive components inAgaricus

bisporus of nutritional, medicinal or biological importance. Mushroom Science16:1-16.

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Reviewed by:

Dr. Gary W. Moorman, Professor of Plant Pathology, Department of Plant Pathology, The

Pennsylvania State University, University Park, PA 16802.

Dr. Donald D. Davis, Professor of Plant Pathology, Department of Plant Pathology, The

Pennsylvania State University, University Park, PA 16802.

Documents

SixSteps to Mushroom Farming